In recent years, a fluorescent light source device has been proposed as a light source device for a projector apparatus (see, for example, Patent Literature 1). The proposed fluorescent light source device has: an excitation light source including a solid light-emitting element, such as a laser diode; and a fluorescent plate that receives excitation light from this excitation light source and outputs fluorescent light.
For example, Patent Literature 1 discloses a fluorescent light source device including: an excitation light-emitting portion whereby excitation light from the excitation light source is converted into and output as collimated light; a transmission-type fluorescent plate that receives the excitation light from the excitation light-emitting portion and outputs fluorescent light; alight condensing optical system that condenses the excitation light from the excitation light-emitting portion on the fluorescent plate; and a collimator optical system that converts fluorescent light from the fluorescent plate into collimated light.
In addition to the light condensing optical system that condenses excitation light, the collimator optical system that converts fluorescent light into collimated light is separately provided to the aforementioned fluorescent light source device. The problem is that it is difficult to reduce the size of the device due to its complicated structure.
A possible means for solving such a problem is to use an optical system that uses a reflective-type fluorescent plate and has both the feature of condensing excitation light and the feature of converting fluorescent light into collimated light.
However, it has been found that such a fluorescent light source device have the following problems:
When a fluorescent material constituting a fluorescent plate receives excitation light, the fluorescent material converts part of its optical energy into thermal energy. Accordingly, when excitation light is excessively condensed and the fluorescent plate is irradiated therewith by the optical system, the temperature of the fluorescent plate rises locally. Temperature quenching thereby occurs to the fluorescent material in the fluorescent plate, which creates difficulty in highly efficiently outputting fluorescent light. In addition, when excitation light is excessively condensed on the fluorescent plate and the fluorescent plate is irradiated therewith, the fluorescent plate deteriorates quickly, and the service life thereof is shortened.
Also, when the focal position of the optical system is moved with respect to the fluorescent plate in the optical axis direction in order to prevent excitation light from being excessively condensed on the fluorescent plate, it is difficult for the optical system to adequately convert fluorescent light output from the fluorescent plate into collimated light. Accordingly, when used as a light source device of a projector apparatus, fluorescent light is not adequately incorporated into a spatial modulating element of the projector apparatus, such as a DMD (Digital Mirror Device). Consequently, achievement of high light utilization efficiency is difficult.